In the European digital cellular system that is now put into the service as the mobile communication system, it is assumed in the GSM (Global System for Mobile Communication) using the frequency of 0.9 GHz band that subscribers will exceed the system capacity in near future. Therefore, the mobile telephone apparatus (hand-held telephone) corresponding to the dual-band system using, in combination with the GSM system, the DCS (Digital Cellular System) 1800 system using the frequency band near 1.8 GHz is requested because this system is similar to the GSM communication system in such a point that the same modulation system GMSK (Gaussian-filtered Minimum Shift Keying) is introduced.
Here, since above two systems (GSM system and DCS1800 system) are almost used in common except for the frequency, it is possible to constitute the hand-held telephone set that is used in common in the GSM/DCS1800 systems by providing only the high frequency unit such as the power amplifier module that can be used for dual band system.
Therefore, in order to achieve the power amplifier module corresponding to the dual-band system, two power amplifier module systems corresponding to each communication system are integrated within the module and are structured to selectively switch each system as required.
FIG. 8 illustrates a schematic structure of the hand-held telephone discussed prior to the present invention. In the same figure, the reference numeral 6 designates a system control unit (CNTU); 10, a blanching filter; 9, a transmitting/receiving antenna corresponding to the dual-band; 1, a first high frequency power amplifier module (RF power Module); 2, a second RF power module; 32, a wide-band amplifier (WAMP); 4, a radio frequency signal processing unit (RFSPU); 7, an operation panel (OP); 8, a transceiver consisting of a speaker (SP) and a microphone (MIC). Moreover, the communication systems that can be used through the switching operation include the GSM system and DCS1800 system.
A radio signal processing circuit 4 is comprised of a modem processing unit, transmitting/receiving IF (intermediate frequency) unit and frequency converting unit (up-/down-converter) or the like and a radio signal (f1 or f2) of any one of the GSM system of 0.9 GHz band or the DCS1800 system of 1.8 GHz band selected is generated and output at the transmitting time. These two kinds of radio transmitting signals f1, f2 are input respectively to the first RF power module 1 and the second RF power module 2.
The RF power module 1 is a power amplifier module corresponding to the GSM communication system and is comprised of an RF power MOSFET (T1) for final stage amplifier, matching circuits MC1 and MC2 consisting of passive elements and inductance element Lc1 for DC choke of drain bias. In this case, the transistor T1 is formed to provide an output, through the switching of a gate voltage to cutoff bias level and predetermined bias level for realizing high efficiency, with the first bias control signal 13 output from the system control unit 6 interlocked with the GSM/DCS1800 selection switch of the hand-held telephone body.
In the same manner, the RF power module 2 is the power amplifier module corresponding to the DCS1800 communication system and is comprised of the RF power MOSFET (T2) for final stage amplifier, matching circuits MC3 and MC4 consisting of passive elements and inductance element Lc2 for DC choke of drain bias. In this case, the transistor T2 is formed to provide an output, through the switching of gate voltage to the cutoff bias level and the predetermined bias level to realize high efficiency, with the second bias control signal 14 output from the system control unit 6 interlocked with the GSM/DCS1800 selection switch of the hand-held telephone body.
The RF power module 1 and RF power module 2 are respectively designed to set the matching with the matching circuits MC1 to MC4 so that the radio signals of the respective communication systems can be amplified effectively.
Thereby, the apparatus is operated as a hand-held telephone set of the GSM system, the bias control signal 13 of the RF power module 1 is set to the predetermined bias level and meanwhile the bias control signal 14 of the RF power module 2 is set to the cutoff bias level. Thereby, it is possible to selectively operate only the RF power module 1 to amplify the GSM radio signal f1 (0.9 GHz band).
When the apparatus is operated as a hand-held telephone set of the DCS1800 system, the bias control signal 14 of the RF power module 2 is set to the predetermined bias level and meanwhile the bias control signal 13 of the RF power module 1 is set to the cutoff bias level and thereby only the RF power module 2 is selectively operated to amplify the DCS1800 radio signal f2 (1.8 GHz band).
The structure explained above is selectively used depending on the setting of communication system by respectively providing the exclusive RF power modules within the apparatus for two communication systems. The RF power modules provided within the apparatus are designed in the optimum manner for respective communication system, assuring economical and effective operation.
Moreover, the RF power module used in the hand-held telephone set satisfies the specifications of the high frequency characteristic determined by each system such as the output power or the like and is also required to satisfy further high efficiency and reduction in size and therefore this RF power module should attain both small size and high efficiency.
Here, the technique to control the harmonics is well known as the technique to realize further high efficiency operation of the power amplifier for transmitter. For example, the Japanese Published Unexamined Patent Application No. SHO 60(1985)-109310 discloses the structure that one end part of the ¼ wavelength transmission line is terminated at a higher frequency, while the other end thereof is connected to an amplifier element and a series resonant circuit to obtain the desired basic waveform signal output from the serial resonant circuit. With this structure, the connecting point of the output side of the amplifying element and ¼ wavelength transmission line is terminated for the basic waveform and odd number order harmonics and thereby the ideal class F operation mode in which a current and a voltage at the output terminal of the amplifying element become zero can be obtained, and high efficiency can also be attained.
The high frequency power amplifier circuit of the related art forms a power amplifier circuit, as illustrated in FIG. 9(a), by connecting the other end of a ¼ wavelength transmission line 34 with one end thereof is terminated for high frequency signal to the output side of an amplifying element 33 and one end of the series resonance circuit 35 and the other end of the series resonance circuit 35 to an output terminal 36. Here, when the amplifying element 33 operates upon input of a basic signal, the voltages are distributed on the ¼ wavelength transmission line 34. FIG. 9(b) illustrates the condition of voltage distribution on the ¼ wavelength transmission line 34. This voltage distribution can be obtained for signal inputs of basic signal and double-frequency signal. In this figure, I indicates the connection part of the ¼ wavelength transmission line 34 terminated to the output terminal of the amplifying element 33, while II indicates the high frequency termination part of the ¼ wavelength transmission line 34. Sine one end II of the ¼ wavelength transmission line 34 is perfectly terminated for high frequency signal, the voltages are applied to the connection part I to open for the basic frequency signal and to terminate for the double-frequency signal. Moreover, above voltage distribution is similar to the third harmonics or higher and the connection part I is opened for all odd number order harmonics as in the case of the basic frequency signal and is terminated as in the case of the double-frequency signal for all even number order harmonics.
However, when the high efficiency technique is applied to the circuit structure of FIG. 8 explained above, a couple of power amplifier modules adding the circuit for harmonics control as explained above are required, resulting in the disadvantage that the circuit configuration becomes large in size.
A method for selectively using the circuits of the RF power module 1 for only GSM system and the RF power module 2 for only DCS1800 system is superior in the point of efficiency, but when the harmonics control circuits are respectively provided for the modules of both GSM system and DCS1800 system in order to realize still higher efficiency, the circuit configuration becomes large, resulting in increase in size of the hand-held telephone set.
Moreover, it is also proposed as a method for reducing the size of the hand-held telephone set for the dual-band system to use the RF power modules for common use in both GSM system and DCS1800 system and form the driver amplifier and RF power module for both communication systems in the single system structure of one-input and one-output. However, this method has the difficulty that efficiency is lowered to a large extent because the output powers are considerably different in two communication systems.
Namely, when the single system structure of one-input and one-output is formed for both communication systems, since the relationship between the radio frequency signal f1 (0.9 GHz band) of the GSM system and the radio frequency signal f2 of the DCS1800 system (1.8 GHz band) is 2×f1=f2, the circuit that is terminated at the drain terminal of the RF power MOSFET for final stage amplifier for 1.8 GHz corresponding to the double-frequency signal of the GSM system is used to execute the harmonics control to realize high efficiency GSM system by utilizing the ¼ wavelength transmission line of the related art. However, the frequency of 1.8 GHz corresponds to the frequency band of the DCS1800 system and therefore when the DCS1800 system is introduced, the output power cannot be obtained.
Moreover, in view of driving the exclusive RF power module for two communication systems, when sufficient wide frequency band to sufficiently cover the frequency difference between the radio frequency signal f1 (0.9 GHz band) of the GSM system and the radio frequency signal f2 (1.8 GHz band) of the DCS1800 system is given to the driver amplifier, since the unwanted harmonics are also amplified, it is liable that unwanted harmonics are radiated from the antenna via the RF power module and this phenomenon will deteriorate a problem in the communication quality.
The present invention has been proposed to solve such problem and it is therefore an object of the present invention to provide a small-size mobile telephone apparatus that assures higher efficiency for the dual-band communication system using in common two-frequency bands and controls leak of unwanted signals.